In the context of the present document, bursts are assemblies of symbols representing data to be transmitted. Each burst is transmitted during a time period which is typically short relative to the latency time between the transmission of two successive bursts by one and the same service. The sequences of bursts from a plurality of services (e.g. different television channels) may be interleaved, but this will not subsequently be of any significance. Each burst comprises a data section (comprising one or more blocks of information symbols) and an error protection section (comprising one or more blocks of redundancy symbols). At the time of transmission, two types of symbol errors may arise: incorrect symbols are received or symbols are lost (or “erased”). The blocks of redundancy symbols constitute an error protection code.
Data transfer by burst proceeds, for example, in the context of a DVB (digital video broadcasting) system.
A conventional solution for generating a block of redundancy symbols of a burst consists in applying a coding function to the block of information symbols of the same burst. The result is “intra-burst” error protection, which allows the receiver to correct transmission errors within the block of information symbols of a received burst. For this approach to work, the burst to be corrected must arrive at its destination. “Intra-burst” protection is used in particular in digital video broadcasting, for example according to the standard DVB-H (digital video broadcasting—handheld). “Intra-burst” protection is not suitable for the erasure of entire bursts in the sequence received bursts. However, such situations are quite frequent for certain communication links, for example between a satellite and a mobile terminal.
Document US 2009/0006927 proposes “inter-burst” protection which makes it possible to remedy the loss of entire bursts. According to the process disclosed in said document, the data packets are grouped according to priority levels. Error correction code words specific to each group are generated on the data packets, belonging to the group, of at least two bursts of a first assembly of bursts. The correction codes thus obtained are transmitted in the error correction section of at least one burst of a second assembly of bursts.
Document US 2010/0031121 also describes an “inter-burst” protection process, in which an error correction code word is calculated on the basis of interleaved data originating from a plurality of bursts of an elementary data stream. Document U.S. Pat. No. 5,870,412 discloses an “interpacket” protection process, in which an error correction code composed of the XOR sum (“OR”-exclusive logic) of a predetermined number (>1) of preceding payload packets is attached to each packet.
Document ETSI TS 102 584 V1.1.1 (2008 December), “Digital Video Broadcasting (DVB); DVB-SH Implementation Guidelines” available on the website of the European Telecommunications Standards Institute (ETSI) describes a an “inter-burst” protection process (see in particular the illustrations on pages 62 and 63). According to this process, each transmitted burst contains an error correction section calculated on the basis of interleaved data from multiple previous bursts. Each burst of datagrams is distributed over B encoding matrices. An error correction code word is calculated for each encoding matrix and attached to a burst of datagrams, optionally after interleaving with one or more other error correction code words. Each item of data is protected just once, i.e. it is used in the calculation of just one error correction code word. Similar encoding processes are also known from ETSI TR 102 993 V.1.1.1 (2011 February) and “A Multi-Burst Sliding Encoding for Mobile Satellite TV Broadcasting” by M. Ismail et al., Research Report No. 6785, INRIA. These documents describe MPE-IFEC processes (producing “inter-burst” protection), in which the error correction code words are interleaved between them before the blocks thus obtained are attached to the bursts of datagrams. As in the previous references, each item of data is protected just once, i.e. it is used in the calculation of just one error correction code word.